The existing process of ammoximation reaction requires the addition of a low-carbon alcohol soluble in water, such as t-butanol as a solvent. However, the selected solvent cannot stably exist in the fuming sulfuric acid system, and separation processes, such as multiple distillations, extractions, etc., should be performed before the rearrangement reaction, resulting that the process is complicated, the energy consumption is large, the stability of the oxime solution is poor, etc. The patent CN200510032184 discloses an improved ammoximation technique using a process of integrating two heterogeneous reactions. The solvent used in the Beckmann rearrangement reaction is the same as the solvent used in the oximation reaction. The solvent can stably exist in a rearrangement system containing the fuming sulfuric acid, and doesn't react itself. Therefore, the pure oxime can be obtained from the oximation product without conventional separation methods such as distillation, extraction, etc. However, the method has drawbacks such as unreasonable raw material reaction ratio, serious waste of raw materials, low conversion rate and the like.
In order to solve the problem, such as separation efficiency of the catalyst, etc., in the ammoximation process, the patent CN021002274 and the patent CN021002282 disclose a continuous setting separation method for ammoximation products and the catalyst. The catalyst is recycled, thereby improving the utilization rate of the hydrogen peroxide and realizing the industrialization of the novel process. However, since the silicon and titanium elements in the titanium-silicon molecular sieve catalyst are easily dissolved and lost in the concentrated ammonia solution of the ammoximation reaction, the continuous and stable circulation of the catalyst may be affected. The patent CN031379141 discloses a method for inhibiting the loss of the catalyst and prolonging the service life of the catalyst. A liquid silicon-containing auxiliary agent is added to the ammoximation reaction system including a silicon-containing catalyst to allow the silicon in the solution to achieve an equilibrium concentration, and thus the loss of the silicon in the catalyst is significantly reduced. However, the above method increases the complexity of the reaction, and introduces new impurities, which increases the difficulty of the oximation reaction, and reduces the conversion rate.
In summary, as for the continuous ammoximation process, the following problems are currently presented: (1) the reaction ratio of the raw materials is unreasonable, the waste of the raw materials is serious, and the conversion rate is low; (2) The concentrated ammonia solution in the ammoximation reaction easily causes the dissolution and loss of the active elements in the catalyst, which affects the continuous and stable circulation of the catalyst.